The proposal builds upon our long-term studies of calcium and magnesium homeostasis in the perinatal period and the diabetic pregnancy. It is designed to examine calcium-magnesium metabolism in infants in insulin dependent diabetic mothers. Infants studied are derived from the Core Clinical Trial of diabetic women randomized into Group I, strict control versus Group II, customary control; and Group III, late entry subjects. In the present proposal, infants of diabetic mothers are further randomized at the time of delivery into-two groups, one given intramuscular magnesium sulfate and one untreated. The hypothesis to be studied is that magnesium deficiency is the major mechanism for hypocalcemia in infants of diabetic mothers, and therefore prophylactic magnesium administration in a clinical trial will prevent neonatal hypercalcemia in such infants. We hypothesize that infants randomized to magnesium sulfate at birth will have higher serum magnesium, calcium, parathyroid hormone, and similar 1,25-dihydroxyvitamin D concentrations at 12, 24 and 72 hours of age when compared with infants randomized to receive no magnesium sulfate. Since hypomagnesemia and hypocalcemia in the neonatal period may be associated with electroencephalographic abnormalities, tetany, convulsions, and cardiac disturbances, and since traditional treatment of neonatal hypocalcemia (i.e. calcium salts) is responsible for many potential complications, magnesium administration at birth could prove to be a safe, simple alternative to calcium therapy. The present study also will take into account major confounding variables of neonatal asphyxia and prematurity, and allow the determination of the contribution of magnesium deficiency to neonatal hypocalcemia.